فصلنامه علوم و مهندسی سطح ایران
پیاپی 48 (تابستان 1400)

In this study, tiles were coated with TiO2 and TiO2-Ag in different weight percentages by sol-gel and immersing method. The structural characteristics of the samples by XRD and EDS showed the rutile phase of TiO2 and Ag2O3. Microstructural studies using FESEM showed that the grain size decrease d with increasing of titanium dioxide and silver nitrate. The antibacterial properties of the samples with different amounts of silver nitrate and titanium dioxide were investigated by two types of gram-positive bacteria Staphylococcus aureus ATCC 6538 and gram-negative bacteria Escherichia coli ATCC 25922 under visible light. The results showed that the percentage of reduction of S. aureus and E. coli bacteria by TiO2-Ag coatings was 99% and 98%, respectively. The wettability behavior of the coatings was obtained by measuring the contact angle. Doping silver nanoparticles with titanium dioxide reduces the contact angle and the samples behavior changes from hydrophilic to super-hydrophilic.

In this study, the aluminum oxide coating was applied on 5083 Aluminum alloy by hard anodizing method in sulfuric acid. M icrostructural investigations showed that anodizing process leads to the formation of porous amorphous alumina coating on the surface of 5083 aluminum alloy. The porosity of the coating surface increases by increasing the anodizing voltage, leading to an increment in the surface roughness. In addition, as the voltage increased, the thickness and hardness of the coating increased due to the higher dissolution rate of the 5083 Al alloy substrate. M icroscopic examinations were indicant of appropriate adhesion of the aluminum oxide coatings. The anodizing process significantly improved the tribological behavior (at least more than 20 times) of 5083 aluminum alloy. M icroscopic analysis showed that the main wear mechanisms of 5083 aluminum alloy were abrasion and delamination and the dominant wear mechanisms in aluminum oxide coatings were adhesive and delamination.

Quench-Polish-Quench(QPQ) is a low temperature process in a liquid salt bath and is used for modifying the surfaces of metals to enhance corrosion and wear resistance. In this research, the effects of the compound and oxide layers on microstructure and corrosion properties of steel CK67 were investigated. The QPQ process was carried out by nitriding at 580°C for 120 minutes, followed by the oxidation treatment at 380°C for 20 minutes. The modified surface was then studied by using optical microscopy (OM ), scanning electron microscopy (SEM ), X -ray diffractometer (XRD), corrosion and microhardness tests. The results show that the surface layer consists of Gamma prime (γ'), iron, magnetite, and epsilon nitride(Ɛ ). Accordingly, the nitriding and the following oxidation treatment led to the enhanced corrosion properties and hardness in comparison to the steel before applying the QPQ process. The most achieved value of hardness was 587 HV which was nearly three times higher than that without the QPQ process. In addition, after 144-hour salt spray testing, corrosion products were observed on the coated surface.

According to the widespread use of aluminum alloys in the oil and gas and petrochemical industries and their low corrosion resistance in corrosive environments, it is necessary to make the surface of these alloys resistant to corrosion using a appropriate coating method. In this research, the coating method in an aqueous environment in an autoclave on the surface of 6061 aluminum alloy was used and its corrosion resistance was investigated. The cleaned samples were placed in an autoclave. Then, by controlling the temperature, time and pressure, an oxide / hydroxide coating was created on the surface. X-ray diffraction (XRD) patterns showed that the coating generally contained an AlO(OH) phase. Scanning electron microscopy (SEM ) images of the coating surface showed that the cubic nanocrystals were densely formed throughout the surface. Vickers microhardness test also showed that the coating was soft and had no effect on the surface hardness. However, the polarization curves show that the corrosion current density of the generated substrates is significantly reduced and the corrosion potential is more positive. As the parameters of autoclave temperature, time and pressure increase, the coating thickness increases and the corrosion current density decreases. It was also concluded that the coating method in the aqueous environment inside the autoclave in liquid and immersed state is a more desirable method due to the higher autoclave pressure than the water vapor state. This indicates that the corrosion resistance of 6061 aluminum alloy has been significantly increased by the use of steam coating.